1. Field of the Invention
The present invention relates to an apparatus for transferring a threading tail of a web from a press section to a dryer section of a papermaking machine. More particularly, the present invention relates to an automatic apparatus for transferring a threading tail of a web such that the tail can be automatically threaded from a press section to a dryer section of a papermaking machine.
2. Information Disclosure Statement
In the papermaking art, excess water is usually pressed from a formed web by passing the formed web between counter-rotating press rolls or a series of counter-rotating press rolls.
Typically, one of the press rolls is a granite roll having a diameter of approximately five foot. Usually, such granite press rolls have a width in the region of 34 foot.
During the pressing operation, the granite press roll rotates at 3,000 to 4,000 feet per minute peripheral velocity, and in the event of a web breakage in the subsequent dryer section or in the starting-up operation, it is necessary to effect a transfer of the pressed web from the granite press roll to and around the downstream dryer section.
In order to carry out the aforementioned transfer, a doctor blade cooperates with the granite press roll such that the full width pressed web is doctored from the rotating granite press roll.
Subsequently, a narrow threading tail approximately 2 to 8 inches in width is cut by means of a water jet or the like disposed upstream relative to the press doctor. The arrangement is such that the threading tail and the remainder of the full width web are doctored from the press roll to a broke pit.
A lead-in roll of the dryer section guides a dryer felt into the vicinity of the press section. The dryer felt thereafter is guided from the lead-in roll to and around a baby dryer or the like of the dryer section.
A skilled operator equipped with an air wand or similar equipment then lifts the threading tail from the granite press roll and endeavors to blow the threading tail into the converging nip defined between a threading rope extending around the baby dryer cylinder such that the tail is threaded from the press roll into and around the dryer section.
Subsequently, when the tail has been threaded through the dryer section and the tail has been guided by the dryer felt out of engagement with the ropes, the threading tail is widened to a full width web such that the full width web is transferred from the press section into the dryer section.
In a more specific prior art transfer mechanism of the aforementioned type, a guide roll is disposed between the lead-in roll and the baby dryer. The lead-in roll includes an annular groove disposed at one end thereof for guiding a threading rope around the lead-in roll. The baby dryer is also provided with a corresponding further annular groove for guiding the threading rope from the lead-in roll to and around the baby dryer.
Similarly, the guide roll is provided with an annular rope groove, and a further rope extends around the annular rope groove of the guide roll and then subsequently around the further annular groove of the baby dryer.
In a threading operation, the operator in fact attempts to thread the tail between the converging nip defined between the two threading ropes. The arrangement is such that the tail is pinched between the converging ropes so that the threading tail is guided through and around each of the dryer cylinders of the drying section.
Those skilled in the art will appreciate the difficulties associated with the aforementioned threading arrangements. Although, a skilled operator may be successful in transferring a tail from a press section to a dryer section in a relatively efficient manner, it is not uncommon for operators to spend several hours during a single day attempting to transfer a web. In the meantime, the pressed web is doctored to broke, and a typical papermaking machine operating to broke costs in the region of $40,000 per hour in lost production.
More specifically, in a prior art threading operation, the operator blows the tail off of the last press roll and away from the doctor blade. By skillfully directing the air out of the blowing device, the tail can be directed towards and into the nip created between the following dryer felt and the first dryer cylinder.
The dryer section speed is then set at the value adequately higher than the press section speed so that the slack in the tail is pulled out and the tail is then tensioned.
Once the tail is stabilized, it is carefully and manually removed from the felt and slowly pulled outward until it enters the nip between two special threading ropes which carry the tail to the end of the dryer section. Once the tail reaches the end of the dryer section, the tail at the press area is manually released and allowed to stabilize again on the dryer felt.
After the tail is running in a stable fashion through the dryer section, the wet end tail cutting device is slowly moved toward the back side of the web so that the tail widens until a full width sheet is running through the dryer section.
The problems experienced with this type of manual operation are that the transfer requires considerable skill, and it cannot always be accomplished consistently and quickly.
Several methods have been proposed in the past to automate this transfer, but none of these methods have been very successful. One such method was suggested in a publication by Scapa-Porrit Ltd. entitled "Felts and Fabrics Sheet Flutter in the Dryer Part". The aforementioned method includes a suction roll which is placed within the first dryer felt run and nipped against the last press roll. The suction in the roll is intended to pull the full width web from the press roll and transfer it into the dryer section. Three problems, at least, exist with the aforementioned approach. The suction roll does not consistently transfer the full width web uniformly across the entire width. Secondly, the draw, which is generally needed to maintain adequate sheet tension, cannot be produced between the nipped rolls. Thirdly, the problem of threading the web through the rest of the dryer section is simply moved from the press section to the dryer section.
Another attempt to automate the transfer is disclosed in West German patent DE 35 24 006 to Valmet. In the aforementioned approach, air jets are used to blow the tail from the press roll onto a conveyor belt in order to thread the tail into the dryer felt nip. After this operation, the tail can be blown off of the felt and into the threading ropes by air nozzles as taught by Kerttula U.S. Pat. No. 4,543,160. The aforementioned patents teach various attempts at automating the operations which are generally accomplished manually. The problems with the aforementioned arrangements are that the devices do not adequately accommodate normal variations in the web release from the press roll. Also, such arrangements do not accommodate for changes in web moisture and changes in local air currents. Additionally, efficient threading of the tail into the rope nip requires the tail to be held flat, in a stable manner without any slack, and air jets are not capable of such threading. Therefore, the results of the aforementioned methods are inconsistent, resulting in inefficient transfers.
Consequently, the present invention seeks to provide an apparatus for transferring a tail of a web from a press section to a dryer section such that the threading tail is transferred automatically without the need for manual intervention.
Therefore, it is a primary objective of the present invention to provide an apparatus for transferring a threading tail of a web from a press section to a dryer section that overcomes the aforementioned problems associated with the prior art arrangements and which makes a considerable contribution to the web transfer art.
Another object of the present invention is the provision of an apparatus for transferring a threading tail of a web which includes a lead-in roll having a suction tail box connected to a source of partial vacuum so that the tail box cooperates with the threading tail.
Another object of the present invention is the provision of an apparatus for transferring a threading tail of a web which includes means for moving a lead-in roll from a first to a second location. The first location is in close proximity to a press roll or even touching the press roll such that when a tail box is connected to a source of partial vacuum, the tail is drawn away from the press roll onto a dryer felt. The second location is spaced from the press roll such that an open draw is established between the press roll and the lead-in roll.
Another object of the present invention is the provision of an apparatus for transferring a threading tail of a web which includes a tail guiding means which contacts the threading tail for urging the tail laterally relative to the lead-in roll.
Another object of the present invention is the provision of an apparatus for transferring a threading tail of a web which includes threading rope means which extend around a lead-in roll. The rope means are disposed such that the tail is moved laterally along the lead-in roll into a nipping relationship relative to the rope means.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.